The art relating to alumina-containing supports, impregnating such supports with various catalytically active metals, metal compounds and/or promoters, and various uses of such impregnated supports as catalysts, is extensive and relatively well developed. As a few of the many exemplary disclosures relating to these fields may be mentioned the following United States patents, all of which are incorporated herein by reference for all purposes as if fully set forth U.S. Pat. Nos. 2,838,444; 2,935,463; 2,973,329; 3,032,514; 3,058,907; 3,124,418; 3,152,865; 3,232,887; 3,287,280; 3,297,588; 3,328,122; 3,493,493; 3,623,837; 3,749,664; 3,778,365; 3,897,365; 3,909,453; 3,983,197; 4,090,874; 4,090,982; 4,154,812; 4,179,408; 4,255,282; 4,328,130; 4,357,263; 4,402,865; 4,444,905; 4,447,556; 4,460,707; 4,530,911; 4,588,706; 4,591,429; 4,595,672; 4,652,545; 4,673,664; 4,677,085; 4,732,886; 4,797,196; 4,861,746; 5,002,919; 5,186,818; 5,232,888; 5,246,569; 5,248,412 and 6,015,485.
While the prior art shows a continuous modification and refinement of such catalysts to improve their catalytic activity, and while in some cases highly desirable activities have actually been achieved, there is a continuing need in the industry for even higher activity catalysts, which are provided by the present invention.
Much of the effort to develop higher activity catalysts has been directed toward developing supports that enhance the catalytic activity of metals that have been deposited thereon. In an overwhelming majority of applications the material chosen for a support is alumina, most often γ-alumina, but silica-alumina composites, zeolites and various other inorganic oxides and composites thereof have been and are employed as support materials. In the case of alumina, various researchers have developed methods for preparing supports having various surface areas, pore volumes and pore size distributions that, when appropriate metals are applied, are particularly suited for catalyzing a desired reaction on a particular feedstock, whether that reaction be directed toward hydrodesulphurization, hydrodemetallation, hydrocracking, reforming, isomerization and the like.
In most cases, the γ-alumina supports are produced by activation (usually calcination) of pseudo-boehmite (AlOOH) starting material. On rare occasions, the support has been generated from one of the heretofore known aluminum trihydroxides (Al(OH)3), Gibbsite, Bayerite or Nordstrandite. When Bayerite or Nordstrandite is used as starting material, the resulting dehydrated alumina has a structure different from the more typical γ-alumina, often referred to as η-alumina; for Gibbsite, the product alumina can be χ-alumina. Each of these transitional aluminas possesses different textures (porosities and surface areas) from the more common γ-alumina. However, they generally suffer from lower thermal stability than γ-alumina; for a specific dehydration and calcination procedure, the loss of surface area for these aluminas is much greater than would be experienced by γ-alumina. U.S. Pat. No. 6,015,485 teaches a way to enhance the texture of γ-alumina supported catalysts by the in-situ synthesis of a crystalline alumina on the γ-alumina base support. From that teaching, higher activity catalysts have been produced.
As an example of the need for higher activity catalysts may be mentioned the need for a higher activity first stage hydrocracking catalyst. In a typical hydrocracking process, higher molecular weight hydrocarbons are converted to lower molecular weight fractions in the presence of a hydrocracking catalyst which is normally a noble metal impregnated silica-alumina/zeolite. State-of-the-art hydrocracking catalysts possess a very high activity and are capable of cracking high volume throughputs. Such catalysts, however, are highly sensitive to contaminants such as sulfur, metals and nitrogen compounds, which consequently must be removed from the hydrocarbon stream prior to the cracking. This is accomplished in first stage hydrocracking processes such as hydrodenitrogenation, hydrodesulfurization and hydrodemetallation. Hydrotreating catalysts utilized in these processes are typically a combination Group VIB and Group VIII metal impregnated alumina substrate. State-of-the-art hydrotreating catalysts, however, are not sufficiently active to allow processing of the same high volume throughputs as can be processed by the hydrocracking catalysts. As such, the first stage hydrocracking processes form a bottleneck in the overall hydrocracking process, which must be compensated, for example, in the size of the hydrotreating unit relative to the hydrocracking unit.